FIG. 8 is a circuit diagram of conventional power supply circuit 500 disclosed in PTL 1. Power supply circuit 500 includes buck-boost DC-DC converter 500A for stepping up or stepping down a DC voltage.
Power supply circuit 500 includes input port 103 connected to commercial power supply 101. Diode bridge 105 is connected to input port 103, and input capacitor 107 is connected in parallel to a subsequent stage of diode bridge 105. Buck-boost converter 500A is also connected to the subsequent stage of diode bridge 105.
Buck-boost converter 500A includes choke coil 109, high-side switching device 11, low-side switching device 113, diodes 115 and 117, and output capacitor 119. Both ends of output capacitor 119 function as output ports 121 of power supply circuit 500. Load 123 is connected to output ends 121.
Power supply circuit 500 includes controller 125, current detector 127, and high-side driver IC 129. Power supply circuit 500 further includes bootstrap capacitor 131 and diode 133 that constitute a bootstrap circuit.
DC driver voltage Vcc is applied to controller 125. Controller 125 generates a switching signal for turning on and off high-side switching device 111 and low-side switching device 113 so that an output current may match a target current.
In the bootstrap circuit shown in FIG. 8, bootstrap capacitor 131 is charged with DC drive voltage Vcc when both of high-side switching device 111 and low-side switching device 113 are turned off. By using this charge, a ground level of a switching signal of high-side switching device 111 is raised to secure a drive voltage to turn on high-side switching device 111.
However, in conventional power supply circuit 500, diodes 115 and 117 generate heat during operation, and cause the entire efficiency of power supply circuit 500 to degrade accordingly.